In this U54 Center Grant application, we propose to expand the capacity of an existing Ligand Assay Core at Northwcstcm University (Jon E. Levine, Director) to meet the assay needs of the U54 Chicago Center for Reproductive Research (CCRR) Center Grant Investigators. The Ligand Assay Core will provide direct assay service, training, consultation, and access to equipment and supplies for hormone and neuropeptide measurements required by projects of Core users. The CCRR Projects 1-4 will all access the Core, and will compensate the Core in proportion to their usage according to a standardized chargeback system. The specific aims of the Ligand Assay Core are as follows: 1. To enhance the cost-effectiveness of hormone and neurotransmitter measurements required by Core users in approved projects. 2. To maintain stringent and consistent quality control standards in all assays. 3. To make available assay procedures that would otherwise be impractical and/or not feasible for use by individual investigators. 4. To develop new assay methods to enhance the projects of Core users.